Armor module

ABSTRACT

An armor module for protecting a surface against an explosively formed projectile (EFP) threat is provided. The armor module is configured for mounting on the surface and comprises at least one armor assembly having a hard layer disposed facing the threat and being configured to fragment the EFP, thus forming residuals of the original EFP threat; a unidirectional fiber layer disposed behind the hard layer; and a catcher layer behind the unidirectional fiber layer, the catcher layer being made of a material exhibiting a level of ballistic protection such that a layer of the material being of the same thickness as the unidirectional fiber layer absorbs at least 20% more energy than is the unidirectional fiber layer for the same threat.

FIELD OF THE INVENTION

This invention relates to an armor module adapted to protect a body froman incoming projectile, in particular against explosively formedprojectile charges (EFP).

BACKGROUND OF THE INVENTION

When designing ballistic armor for protecting, for example, a vehicle,consideration must be given to the type of projectile against which thearmor must protect.

An important consideration which must be taken into account whendesigning ballistic armor is the weight per coverage area of the armor.Theoretically, armor can be constructed to protect against almost anythreat or combination of threats. However, the resulting weight of theminor needed for such protection should be practical for the intendeduse. For example, when designing armor for vehicles such as trucks,armored infantry fighting vehicles, or armored personnel carriers, heavyarmor will negatively impact the maneuverability and fuel efficiency ofthe vehicle, and will be more difficult to replace when necessary. Heavyarmor can exceed the gross vehicle weight (GVW) set by the vehiclemanufacturer and therefore cannot be used for such vehicle.

One type of threat is referred to as an explosively formed projectile(EFP). An EFP has a metal liner in the shape of a shallow dish with anexplosive material behind it. When the explosive material is detonatedthe force of the blast presses the liner plastically into any of anumber of configurations, depending on how the plate is formed and howthe explosive is detonated. For example, the liner may be molded into anarrow rod, a “fist”, a plate (dish), or segmented rod.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is an armormodule for protecting a surface against an explosively formed projectile(EFP) threat, the armor module being configured for mounting on thesurface and comprising at least one armor assembly having:

-   -   a hard layer disposed facing the threat and being configured to        fragment the EFP, thus forming residuals of the original EFP        threat;    -   a unidirectional fiber layer disposed behind the hard layer; and    -   a catcher layer behind the unidirectional fiber layer, the        catcher layer being made of a material exhibiting a level of        ballistic protection such that a layer of the material being of        the same thickness as the unidirectional fiber layer absorbs at        least 20%, and according to another example at least 30%, more        energy than is the unidirectional fiber layer for the same        threat (i.e., under the same ballistic conditions, including the        same type of projectile at the same velocity).

It will be appreciated that hereafter in the specification and claimsthe terms “in front” and “behind” refer to directions with reference tothe expected direction of the threat, with “in front” meaning closer tothe expected direction of the threat, and “behind” meaning farther fromthe expected direction of the threat.

The specific weight of the catcher layer may be no more than 90%, andaccording to some examples no more than 85%, of that of theunidirectional fiber layer.

The fibers constituting the unidirectional fiber layer may constitute aportion of a laminate, the tensile strength of most of the fibersexceeding the force required to remove them from the laminate.

The unidirectional fiber layer may comprise aramid fibers.

The catcher layer may comprise a plurality of pressed fibers, which maybe arranged unidirectionally, and which may be made from a materialselected from the group comprising polypropylene and high densitypolyethylene. The catcher layer may comprise at least two times, andaccording to some example at least four times, as many fibers per unitthickness thereof than does the unidirectional fiber layer. In addition,the fibers of the catcher layer may be characterized by a specifictensile strength which is at least 10% greater than those of theunidirectional fiber layer.

The material of the catcher layer may be more sensitive to an elevatedtemperature of an impinging threat than is the material of theunidirectional fiber layer, i.e., the catcher layer may exhibit areduced level of ballistic protection against a projectile having anelevated temperature associated with residuals of the EFP, theunidirectional fiber layer exhibiting a level of ballistic protectionwhich remains essentially unchanged, or significantly less reduced asthe catcher layer, at that temperature.

The hard layer may be provided with a backing layer, which may comprisean at least partially or fully woven aramid material, facing the catcherlayer, each of the hard, backing, and catcher layers being characterizedby a ballistic impedance such that the ballistic impedance of thebacking layer is lower than that of the hard layer and higher than thatof the catcher layer. It will be appreciated the ballistic impedance ofa material is defined as the product between its specific density ρ andthe speed of sound through the material.

The hard layer may comprise a material selected from the groupcomprising high-hardness steel and ballistic ceramic.

The armor assembly may further comprise a stand-off between theunidirectional fiber and catcher layers, the stand-off being free ofmaterial of the module.

The armor module may further comprise one of the armor assembliesdisposed in front of another of the armor assemblies.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carriedout in practice, an embodiment will now be described, by way of anon-limiting example only, with reference to the accompanying drawings,in which:

FIG. 1 is a partial cross-sectional view of one example of an armormodule according to the present invention mounted to the hull of avehicle.

DETAILED DESCRIPTION OF EMBODIMENTS

As illustrated in FIG. 1, there is provided an armor module, which isindicated at 10, which is designed to defeat an explosively formedprojectile (EFP) threat, which is indicated at 5 in its expecteddirection of travel toward the armor module. The module is configuredfor mounting on an armored vehicle having a hull 12 constituting asurface to be protected, which, in the present example, constitutes abase armor. The hull may be armored and thus exhibit a level ofprotection which allows it defeat KE threats i.e. fragment andpenetrators, which are much less effective than EFP. It may, forexample, comprise a layer of high-hardness steel disposed in front of aspall liner, which may comprise one or more of an aramid material, ahigh density polyethylene material, or any composite liner material. Thehull 12 exhibits a level of protection, and the minor module is designedsuch that any residuals of the EFP exiting it are within the level ofprotection of the hull 12.

The armor module 10 comprises a primary armor assembly 14 in front of asecondary armor assembly 16. The layers of the armor module are designedsuch that the fragments exiting therefrom are within the level orprotection of the hull 12, i.e., they can be defeated thereby.

The primary armor assembly 14 comprises a hard layer 22 constituting astrike face, which may be made of high-hardness steel, and is positionedso as to face the EFP 5, i.e., at the front-most position of the armor,when the armor module 10 is mounted to the hull 12. Alternatively, itmay be made of ceramic pellets, or any other material configured tofragment an impinging EFP threat into residuals. An adhesive sub-layer24, which may comprise a fiber-reinforced adhesive, is applied to thebackside (i.e., non-threat-facing side) of the hard layer 22, and isused to attach a backing layer 26 thereto. The adhesive may comprise athermoplastic and/or thermoset material, or any other appropriatematerial.

The backing layer 26 may be made of a woven aramid material, such asthat sold under the trade name K3000 may be disposed behind the strikeface 22. The ballistic impedance (which is defined as the productbetween a material's specific density ρ and the speed of sound throughthe material, and is useful for quantifying the propagation of ashockwave through a material, for example due to a ballistic impact) ofthe backing layer 26 may be closer to that of the hard layer 22 than anyof the other layers of the primary armor assembly. This limits thedamage to the hard layer 22 as the shockwave due to impact of a threatthereupon crosses between layers.

A unidirectional fiber layer 28 made of a material comprisingunidirectional aramid fibers formed as part of a laminate, such as GoldShield® made by Honeywell, is disposed behind the backing layer 26. Theunidirectional fiber layer 28 is designed such that fibers thereofenvelop a residual of the fragmented EFP 5 which pass therethrough, andremain enveloping it as it exits the layer. This may be accomplished,for example, by ensuring that the tensile strength of the fibers exceedsthe force required to remove them from the laminate. With such a design,when fibers of the unidirectional fiber layer 28 are struck by aresidual, they are removed from the laminate and remain on the residualbefore they undergo tensile failure. As the fibers remain envelopedaround the residual, they serve to thermally insulate it as in entersthe next later. The significance of this will be explained below.

The hard layer 22, backing layer 26, and unidirectional fiber layer 28together constitute a strike layer, which functions to disrupt the EFP,e.g., by spreading its impact, and preventing secondary fragmentationthereof.

An optional primary standoff 30 may be provided behind theunidirectional fiber layer 28. The standoff gives allows space for thefragments of the disrupted EFP to disperse.

A catcher layer 31 is provided behind the unidirectional fiber layer 28(behind the primary standoff 30 in a case where it is provided) Itcomprises one or more pressed polypropylene sub-layers 32. Thepolypropylene may be, for example, similar to that sold under the tradename Tegris™, sold by Milliken & Company. The polypropylene may behigh-tenacity and it may be provided as unidirectional (UD) or plainweave of strips made of UD fibers. The catcher layer 31 constitutes anabsorbing/diverting layer, which functions to absorb/divert fragments ofthe disrupted EFP from the previous layer.

Ideally, a single thick polypropylene sub-layer 32 is to be provided;however, due to current manufacturing limitations of high pressurepressing, several of such sub-layers may be provided in order to reach adesired thickness when combined. (It will be appreciated that if theselimitations would be overcome, a single polypropylene sub-layer 32 maybe provided.) When a unidirectional polypropylene is provided, thedirections of adjacent layers may be parallel to one another or at anangle to one another. Although no adhesive is necessary between adjacentlayers, a polypropylene resin may be provided between adjacent layers.

Alternatively, the catcher layer 31 comprises one or more high densitypolyethylene layers. In such a case, the thickness of the layer could bereduced without impacting the overall weight of the layer.

The design of the catcher layer 31 is based on that of theunidirectional fiber layer. For example:

-   -   The material of the catcher layer 31 exhibits a level of        ballistic protection which is at least 20% higher than that of        the unidirectional fiber layer 28, i.e., a layer of the material        of the catcher layer which is of the same thickness as that of        the unidirectional fiber layer absorbs at least 20% more energy        of one of the residuals than the unidirectional fiber layer        absorbs for the same residual at the same speed, as is well        known in the art. In addition, the catcher layer 31 may be made        of a material which exhibits a level of ballistic protection        which is at least 30% higher than that of the unidirectional        fiber layer 28.    -   Both the unidirectional fiber layer 28 and the catcher layer 31        may comprise pressed fibers within a laminate. The density of        the pressed fibers of the catcher layer 31 may be at least four        times greater than that of the unidirectional fiber layer 28;        i.e., the catcher layer may comprise four times as many fibers        per unit thickness than does the unidirectional fiber layer.        This may be accomplished, for example, by providing different        sized fibers for the two layers, and/or by providing a more        compressed material for the catcher layer 31.    -   The fibers of the catcher layer may exhibit a specific tensile        strength (i.e., tensile strength per unit cross-sectional area        of the fiber) which is at least 10% greater than that of the        fibers of the unidirectional fiber layer 28, as is well known in        the art.    -   The catcher layer 31 may be sensitive to an elevated temperature        of an impinging threat, i.e., it may provide a reduced level of        ballistic protection against a projectile having an elevated        temperature associated with residuals of the EFP; i.e., the        level of protection of the catcher layer against residuals which        are at an elevated temperature due to their recent fragmentation        from an EFP is reduced compared to its level of protection        against residuals at a lower temperature, as is well known in        the art. The level of ballistic protection exhibited by the        unidirectional fiber layer 28 is substantially unchanged, or        reduced less, at this temperature compared to that exhibited at        lower temperatures. Thus, the fibers of the unidirectional fiber        layer 28 which envelop the residual even after it exits the        unidirectional fiber layer serve to thermally insulate it, thus        enabling the catcher layer 31 to provide a higher level of        ballistic protection thereagainst.

The secondary armor assembly 16 comprises a secondary hard layer 18comprising a segmented ceramic sub-layer 34, which may be similar tothat sold under the trade name SMART™ by Plasan, and which is described,for example, in co-pending Israel patent applications IL149591,IL169230, IL190360, and IL182511, the contents of which are incorporatedherein by reference. Ceramic pellets of the segmented ceramic sub-layer34 may each have cylindrical, hexagonal, or any other desiredcross-section, and they may be provided as capped or non-cappedelements.

A secondary backing layer 36, for example made of a woven aramidmaterial such as K3000, may be provided behind the secondary hard layer.In addition, other layers, such as a high-harness steel sub-layer 38, anadditional secondary backing layer 40 made of a woven aramid materialsuch as K3000, and a secondary unidirectional fiber layer 42 made of aunidirectional aramid material, such as Gold Shield®, may be provided.

The secondary armor assembly 16 comprises a polypropylene secondarycatching layer 44, which may be similar to the polypropylene sub-layer32 of the catcher layer 31 of the primary armor assembly 14.

Either of the catching layers 31, 44 may alternatively comprise one ormore high density polyethylene layers instead of or in addition to apolypropylene layer. In such a case, the thickness of the layer could bereduced without impacting the overall weight thereof.

The hull 12 may comprise a high-hardness steel layer 46, with a spallliner 48, for example made of K3000 or UD aramid, high densitypolyethylene, a composite liner material, or a combination thereof,therebehind.

The armor module 10 may be mounted to the hull 12 by any appropriatemeans, for example with mounting rods 50. A mounting standoff 52 may beprovided between the armor module 10 and the hull 12. This standoffaccommodates a non-uniform hull profile, for example allowing the module10 to be mounted to the hull 12 without being disturbed by membersprojecting therefrom, and further allows for fragments exiting the armorto disperse before impacting on the hull strike face. The mountingstandoff 52 may be smaller or larger than the primary standoff 30.

A non-limiting example of an armor module 10 is summarized in Table 1below, with reference numerals provided, which correspond to those usedin the text:

TABLE 1 ARIAL THICK- TOTAL DENSITY NESS WEIGHT LAYER NAME MATERIAL(kg/m²/mm_(thickness)) (mm) (kg/m²) Hard Layer 22 HH Steel 7.85 10 78.5Backing Layer 26 K3000 1.2 5 6 Unidirectional Fiber Gold Shield 1.4 2535 Layer 28 Primary Standoff 30 None N/A 40 0 Catcher Layer 31 Tegris0.78 156 121.68 Secondary Hard SMART 3.32 17 56.44 Layer 18 SecondaryBacking K3000 1.2 3 3.6 Layer 36 Steel Sub-Layer 38 HH Steel 7.85 3.225.12 Additional K3000 1.2 4 4.8 Secondary Backing Layer 40 SecondaryUnidirec- Gold Shield 1.4 10 14 tional Fiber Layer 42 Secondary CatchingTegris 0.78 52 40.56 Layer 44 Mounting Stand- None N/A 25 0 off 52 Hull10 HH Steel 7.85 10 78.5 K3000 1.2 15 18

It can be seen from Table 1 that the total weight of the armor module is385.7 kg/m². For comparison, conventional armor modules which offer thesame level of ballistic protection against an EFP threat may have aweight which is significantly higher, such as approximately 1040 kg/m²for a rolled homogeneous armor (RHA), or approximately 650 kg/m² for aconventional layered metal technology.

Those skilled in the art to which this invention pertains will readilyappreciate that numerous changes, variations and modifications can bemade without departing from the scope of the invention mutatis mutandis.For example, additional standoffs may be provided between other layers,for example between the secondary strike layer 18 and the secondaryabsorbing/diverting layer 20, etc.

The invention claimed is:
 1. An armor module for protecting a surfaceagainst an explosively formed projectile (EFP) threat, said armor modulebeing configured for mounting on said surface and comprising at leastone armor assembly comprising: a hard layer disposed facing the threatand being configured to fragment the EFP; a unidirectional fiber layerdisposed behind said hard layer; and a catcher layer behind saidunidirectional fiber layer, said catcher layer being made of a materialexhibiting a level of ballistic protection such that a layer of saidmaterial being of the same thickness as said unidirectional fiber layerabsorbs at least 20% more energy than said unidirectional fiber layerfor the same threat.
 2. An armor module according to claim 1, whereinthe specific weight of said catcher layer is no more than 90% of that ofthe unidirectional fiber layer.
 3. An armor module according to claim 1,wherein the fibers in said unidirectional fiber layer constitute aportion of a laminate, the tensile strength of most of the fibersexceeding the force required to remove them from the laminate.
 4. Anarmor module according to claim 1, wherein said unidirectional fiberlayer comprises aramid fibers.
 5. An armor module according to claim 1,wherein said catcher layer comprises a plurality of pressed fibers. 6.An armor module according to claim 5, wherein said fibers of the catcherlayer are arranged unidirectionally.
 7. An armor module according toclaim 5, wherein said plurality of pressed fibers of the catcher layerare made from a material selected from the group consisting ofpolypropylene and high density polyethylene.
 8. An armor moduleaccording to claim 5, wherein said catcher layer comprises at least twotimes as many fiber layers per unit thickness thereof than does theunidirectional fiber layer.
 9. An armor module according to claim 5,wherein the fibers of said catcher layer are characterized by a specifictensile strength which is at least 10% greater than those of theunidirectional fiber layer.
 10. An armor module according to claim 1,wherein the material of said catcher layer is more sensitive to anelevated temperature of an impinging threat than is the material of theunidirectional fiber layer.
 11. An armor module according to claim 1,wherein said hard layer is provided with a backing layer facing saidcatcher layer, each of said hard, backing, and catcher layers beingcharacterized by a ballistic impedance such that the ballistic impedanceof said backing layer is lower than that of the hard layer and higherthan that of the catcher layer.
 12. An armor module according to claim11, wherein said backing layer comprises an at least partially wovenaramid material.
 13. An armor module according to claim 1, wherein saidhard layer comprises a material selected from the group consisting ofhigh-hardness steel and ballistic ceramic.
 14. An armor module accordingto claim 1, wherein said armor assembly further comprises a stand-offbetween said unidirectional fiber and catcher layers, said stand-offbeing free of material of the module.
 15. An armor module according toclaim 1, further comprising at least two armor assemblies, wherein oneof said armor assemblies is disposed in front of another of said armorassemblies.